Numerous processes are known for obtaining yarns from two or more synthetic polymer components, having a cross section in which one of the components separates into at least two segments of the other component, whereby these segments retain their shape and location in the cross section along the yarn.
Okamoto, in an article entitled "Ultra-Fine Fiber and Its Application", Japan Textile News, November 1977, pp. 94-97 and December 1977, pp. 77-81, summarized known techniques for making fine-denier fibers and in particular, the ultra-conjugate (converging) fiber spinning method (Integral Fiber's Method). The fiber produced is described as having "islands-in-a-sea".
U.S. Pat. No. 3,531,368 illustrates the details of several types of nozzles referred to in the aforesaid Okamoto article and describes a process for the manufacture of a matrix microfilament yarn wherein a great many very fine microfilaments (segments) of component A are surrounded by a matrix component B and separated from each other by the latter. This type of structure is obtained by first pre-molding bicomponent structures of core-skin or side-by-side structure, collecting a plurality of such pre-formed structures in a funnel-like decreasing chamber opening into a spinning orifice and extruding through the spinning orifice. Both the mutual alignment of the segments over the cross section of the finished yarn and the separation of the segments by the matrix components is random. Special cross section geometries cannot be made reproducibly.
U.S. Pat. No. 3,692,423 also shows yarn cross sections wherein a plurality of segments are separated by a matrix component and further illustrates the "islands-in-a-sea" type fiber similar to that described in U.S. Pat. No. 3,531,368, the improvement comprising limiting the angle, .theta., of the funnel-shaped space converging to each spinning orifice, to 75.degree.. U.S. Pat. No. 3,692,423 further relates to the production of sheath-core or side-by-side filaments where the filaments are merged prior to the spinning orifice. With these known devices, the polymer components are supplied in such a manner that one component first flows out from the axial cavity of a feed element into a passage fed peripherally with a second component whereby the two components are combined in sheath-core or side-by-side fashion and pass through a spinning orifice.
U.S. Pat. No. 3,814,561 describes a process for the manufacture of yarns composed of several segments, whereby component B is supplied axially through a passage consisting of at least two slits to form thin layers and component B is laterally supplied through ducts. Patentees indicate, at column 8, lines 5-12, that obtaining yarns with three, five or more segments (with the exception of six segments) is difficult. Moreover, the spinning heads described in this patent are also difficult to make and conversion of the spinning heads from one yarn cross section to another, e.g. from four segments to six segments, is practically impossible.
Finally, in U.S. Pat. No. 3,540,080 a great many yarn cross sections having two or three components, composed of different polymer components, are disclosed. In most cases, a core component will be surrounded by a matrix component. Although it is the objective of many recent developments in the area of multicomponent yarns, these yarns cannot be separated either by mechanical or chemical aftertreatment into a yarn bundle of extremely fine filaments and/or fibers.